The present invention relates generally to magnetic chip detectors that detect the presence of wear debris in a stream of lubricant. More particularly, the invention relates to a mechanism for retaining a removable probe within a housing of the chip detector.
Bearing and gear failures in gas turbine engines, helicopter gear boxes, and many other types of oil-wetted machinery are typically preceded by the production of wear-related debris. Wear debris is usually produced well in advance of a catastrophic failure of a defective component. Wear debris is typically carried by the machine""s lubricating oil toward a sump or a filter within the machine. The debris can be intercepted and collected by a chip detector as it is being transported in this manner. Periodic inspection of the chip detector can thus provide an indication of an impending component failure.
Magnetic plugs (also referred to as xe2x80x9cchip collectorsxe2x80x9d) and electric chip detectors are the most commonly used types of chip detectors. Chip collectors comprise a probe having a magnetic element. The probe is typically mounted within some type of housing that is securely fixed to a host component, i.e., a component or machine in which the chip detector is utilized. The probe is periodically removed from the host component so that the magnetic element can be inspected for any accumulation of wear debris.
Electric chip detectors also collect wear debris. In addition, electric chip detectors provide an external, electrically-generated indication of the presence of such debris. Electric chip detectors do not require inspection at pre-determined intervals. These types of chip detectors are usually removed and inspected whenever an external signal (a so-called xe2x80x9cchip lightxe2x80x9d) has been activated.
The periodic inspection of chip detectors can present operational drawbacks. For example, many type of machines and mechanical systems utilize multiple chip detectors to identify the location of an incipient component failure. The use of multiple chip detectors allows a defective component or module within the machine or system to be replaced (as opposed to replacing the entire machine or system). The regular inspection of multiple chip-detectors, however, can be a time-consuming maintenance requirement if the chip-detector probes are not specifically designed for quick removal and reinstallation. Furthermore, maintenance personnel must often inspect chip detectors outside, under adverse weather conditions, and within strict time constraints. For example, chip detectors on the engines of commercial airliners must often be inspected during limited turnaround times between flights, while the aircraft is parked on an outdoor ramp.
Thus, chip detectors are often equipped with some type of quick-disconnect mechanism that secures the probe to the housing of the chip detector. Quick-disconnect mechanisms secure the probe in a manner that facilitates removal and reinstallation of the probe with a minimal expenditure of time and labor. Quick-disconnect mechanisms usually comprise a plurality of retaining pins or blades disposed on a surface of the probe. The pins or blades engage corresponding grooves or slots formed in the housing.
Common quick-disconnect mechanisms have a number of substantial disadvantages. For example, quick-disconnect mechanisms are susceptible to excessive wear. This problem stems from the relatively small size of the retaining pins and blades. Specifically, the limited surface area of the pins and blades concentrates the probe-retention forces. This concentration, combined with the vibration normally generated by most machinery, typically produces substantial wear of the pins and the blades. Such wear can eventually cause the pins or the blades to fail. Pin and blade failures can lead to an ejection of the probe, and an ensuing loss of lubricating oil. Ejections of chip-detector probes in this manner on aircraft engines have been known to cause costly and potentially dangerous service disruptions, e.g., in-flight engine shutdowns.
Furthermore, the use of retaining pins or blades complicates the manufacturing process for the probe. Also, pins and blades are usually not visible once the probe has been inserted in the housing. Hence, the probe installer does not receive a positive visual indication that the probe has been properly installed.
Alternatively, the probe and the housing can be coupled using threads. Coupling the probe and the housing in this manner alleviates the wear-related problems associated with quick-disconnect locking mechanisms. Specifically, the use of threads substantially reduces relative movement between the contact surfaces on the probe and the housing, and thereby reduces the wear produced by such movement.
Threaded probes present substantial operational disadvantages. In particular, threaded probes must typically be secured in place through the use of lock wire. Lock wire must be removed and installed manually, each time the probe is inspected. The removal and installation of lock wire requires a substantial expenditure of time and labor. Furthermore, lock wire can be installed improperly and, in extreme cases, a probe may inadvertently be reinstalled without any lock wire whatsoever. The need to perform probe inspections within strict time constraints, and under less-than optimal working conditions, increases the possibility that lock wire will not be properly installed following a probe inspection. In addition, lock wire cannot be reused, and is therefore discarded each time a probe is inspected. The residual lock wire produced in this manner can create a so-called FOD (foreign object damage) hazard to the host component if the residual wire is not properly disposed of.
The above-described problems have been apparent for many years. Thus, a long-felt need exists for a chip-detector having a probe-locking mechanism that is resistant to wear, and that allows the probe to be removed and installed with a minimal expenditure of time and labor. In addition, the locking mechanism should make it difficult to install the probe without properly securing the probe to the housing. Furthermore, a locking mechanism which provides a positive visual or tactile indication that the probe has been secured is highly desirable. Optimally, the locking mechanism provides these advantages without adding substantially to the parts count or the manufacturing complexity of the chip detector. The present invention is directed to these and other goals.
An object of the present invention is to provide a chip-detector assembly having improved probe-retention features. A presently-preferred embodiment of the chip-detector assembly comprises a housing, a probe that is capable of being coaxially coupled to the housing, and a locking mechanism. The locking mechanism comprises a plurality of elongated tangs for controlling an amount of torque required to couple the probe to the housing.
The locking mechanism preferably comprises a sleeve member and a locking ring. The sleeve member is fixedly coupled to at least one of the housing and the probe. The sleeve member has a plurality of contact surfaces disposed along a circumference of the sleeve member. The locking ring is fixedly coupled to at least one of the housing and the probe. The locking-ring tangs extend from a portion of the locking ring, and are radially spaced from a central axis of the housing. The tangs engage the sleeve-member contact surfaces when the probe is coupled to the housing.
Preferably, the tangs securely engage the sleeve-member contact surfaces when a torque about equal to or less than a predetermined amount is applied to the probe. The tangs preferably slip over the sleeve-member contact surfaces when a torque greater than the predetermined amount is applied to the probe. The probe thus remains coupled to the housing unless a torque greater than the predetermined value is applied to the probe.
A further object of the invention is to provide a chip-detector assembly having a threaded probe that is retained in a housing without the use of lock wire. In accordance with this object, a presently-preferred embodiment of the chip-detector assembly comprises a housing that includes a threaded inner surface. The chip-detector assembly also comprises a probe having a grip, and a mounting portion coupled to the grip. A plurality of threads are disposed on the probe mounting portion. The mounting portion threadably engages the housing inner surface in response to a torque applied to the grip. The probe also includes a magnetic element coupled to the mounting portion. The chip-detector assembly further comprises a locking mechanism as described above. The locking mechanism causes the probe mounting portion to remain threadably coupled to the housing inner surface unless a torque greater than a predetermined value is applied to the probe.